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Design of O-Ring Seals.  Primary Source of information Design of O-Ring Seals.

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Presentation on theme: "Design of O-Ring Seals.  Primary Source of information Design of O-Ring Seals."— Presentation transcript:

1 Design of O-Ring Seals

2  Primary Source of information Design of O-Ring Seals

3  Can be used for static and dynamic applications  Compact – need very little space - light weight  Easy to incorporate into design  Do not require high accuracy  Simple design rules  Easy to install or remove  Easy to service  Available in many standard sizes, materials Why O-Rings?

4  Wide range of operating temperatures  Wide range of operating pressures  Good durability and abrasion resistance  Many O-ring materials for a wide range of chemicals  Their failure or deterioration is gradual  Inexpensive Why O-Rings?

5  Temperature (typically between -40 and 400 degrees F)  Rotary speeds ( not to exceeding 1500 feet per minute)  For a 2 inch shaft, it is 3000 rpm  Vulnerable to sharp edges  Require small clearances Limitations of O-rings

6 O-Rings

7  Nitrile (Buna-N)  Variety of trade names  Copolymer of butadiene and acrylonitrile  Most widely used and economical elastomer  Temperature Range: Standard Compound: -40° to +257°F  Hardness (Shore A): 40 to 90 Popular O-ring materials

8  Excellent resistance to  petroleum-based oils and fuels  silicone greases  hydraulic fluids  water and alcohol  High tensile strength  High abrasion resistance Popular O-ring materials Nitrile (Buna-N)

9  Applications  Oil resistant applications  Low temperature uses  Off-road equipment  Automotive, marine, aircraft fuel systems Popular O-ring materials Nitrile (Buna-N)

10  Viton ® / FKM: Fluorocarbon (Viton ® ) exceptional resistance to chemicals, oils, temperature extremes (-13°F to +446°F), low compression set. Applications include: aircraft engines, automotive fuel handling systems, and chemical processing industries. Viton ® / FKM:  Ethylene-Propylene / EPDM: EPDM has excellent resistance to heat, water and steam, alkali, mild acidic and solvents, ozone, and sunlight with a temperature range of (-40ºF to +275ºF); but it is not recommended for gasoline, petroleum oil and grease, and hydrocarbon environments. Ethylene-Propylene / EPDM: Other O-ring Materials

11  Fluorosilicone / FVMQ: Fluorosilicone (-75º to +400ºF) combines the good high and low temperature stability of silicones with the fuel, oil, and solvent resistance of fluorocarbons. FVMQ is used for aerospace fuel systems, auto fuel emission control systems. However, due to relatively low tear strength, high friction and limited abrasion resistance of these materials, they are generally not used in dynamic applications. Fluorosilicone / FVMQ: Other O-ring Materials

12  Silicone / VMQ: Superior as static seals in extreme temperature conditions. Standard compounds handle operating temperatures -85º to +400ºF. Silicone compounds are popular in food and medical applications because they are clean and do not impart odor or taste. Special Phenyl silicones can be used down to -148°F. Silicone / VMQ: Other O-ring Materials

13  Neoprene ® / CR: Neoprene (-40º to +250ºF) features good resistance to petroleum oils, ozone, sunlight, relatively low compression set, good resilience and physical toughness. It is the preferred sealing material for the refrigeration industry because of its resistance to ammonia and Freon Neoprene ® / CR: Other O-ring Materials

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17  The O-ring Specifications  Size (inside diameter)  1/32 to 26 inches  CS (Cross-Section)  1/32 to ¼ inch  Rigidity (Hardness)  Material O-Ring Seal Design

18  Standard  AS568  ISO 3601  Example  AS016-70N Nitrile O-ring  (AS Size CS x ID) O-ring Standards

19 O-ring Search Tools

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21  Measured on Shore-A hardness index  Shore 20A = Rubber Band  Shore 40A = Pencil Eraser  Shore 60A = Car Tire Tread  Shore 70A* = Running Shoe Sole  Shore 80A = Leather Belt  Shore 100A = Shopping Cart Wheel O-Ring Hardness

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23 O-Ring Properties  Fluid resistance  Hardness  Toughness  Volume change (swell / shrinkage)  Compression set  Thermal effects  Resilience  Deterioration  Corrosion  Permeability  Coefficient of friction  Coefficient of thermal expansion  Compression set relaxation  Tensile strength  Elongation  Tear resistance / Abrasion resistance

24  The Gland (Groove + Spacing)  Depth of groove  Width of groove  Diameter of bore and piston  Surface finish  Tolerances O-ring Seal Design

25 Static Seals Static Axial Seal (Face Seal)

26 Static Crush Seal Static Seals

27 Static Radial Seal (Piston Seal) Static Seals

28  Reciprocating Seals Dynamic Seals

29  Rotary Seals Dynamic Seals

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31  Stretch should be less than 5% on the O-ring I.D.  Groove depth must be smaller than the O-ring CS  O-ring should not completely fill the gland  Between 75% and 90%  Static seal CS should be compressed from 10% to 40%  Dynamic seals should be compressed from 10% to 30% General Design Guidelines

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33  Axial Seal Design of Axial Seal

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35  Design a groove for a 1.5 inch diameter Internal pressure O-ring  O-ring : -029 (ID: /-.013) (W:.07 +/-.003)  Material: Buna-N  Hardness: 70 Shore-A  A: (-0, +.005)  G:.125 (-0, +.01)  H:.049 (-0,+.005) Example Design

36  Checking resulting compression  Compression (squeeze) = W - H  Min. Comp. = W min - H max  Min. Comp. = in (18.5%)  Max. Comp. = W max - H min  Max. Comp. = in (34.3%) Example Design

37  Radial Static Piston Seal Radial Seal

38  Design a groove for a 0.7 inch diameter piston ring  O-ring : -029 (ID:.614 +/-.009) (W:.07 +/-.003)  Material: Buna-N  Hardness: 70 Shore-A  A:.746 (-0, +.002)  B:.745 (-.001, + 0)  C:.638 (-.001,+ 0) Example Design

39  Checking compression  Comp = W – 0.5(A - C)  Min. Comp = W min – 0.5(A max – C min )  Min. Comp. = in (17.1%)  Max. Comp. = in (26.0%)  Also check  Extrusion gap  Stretch  Squeeze Example Design

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41  Radial Static Rod Seal

42  Static Crush Seal

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44 Dynamic Seals

45 Gland Design For Dynamic O-ring Seals

46 Reciprocating Motion

47 The O-ring’s O.D. is larger than the cylinder bore diameter. Peripheral squeeze is applied to the O.D. as the O-ring is installed into the bore. Incoming air pressure forces the O-ring against the walls sealing

48  Advantage  Greatly reduced breakout friction  Longer seal life  Limitations  Air pressure less than 200 psi in pneumatic cylinders  In hydraulic systems small amount of leakage must be permissible  Floating O-rings are NOT suitable as rod seals Floating O-Rings

49 Alternatives to O-Rings U-cup Seals  O-rings have a tendency to roll and move in reciprocating motions  U-cups create more sealing as the pressure increases  U-cups require less precision for the associated hardware

50 Alternatives to O-Rings U-cup Seals

51 Typical Applications

52 Buffer Seal Buffer seals are one-way seals that protect rod seals from pressure spikes yet allow fluid (lubricant) to reach the main seal

53 Rotary Seals

54 Due to centrifugal force and Gough-Joule effect rotary O-rings are only installed in the housing not on the shaft

55 When an elastomer is stretched and heated, it will contract. Gough-Joule effect

56 Rotary O-Ring Limitations  O-ring seals are NOT recommended for rotary applications under the following conditions:  Pressures exceeding 900 psi  Temperatures lower than -40° F or higher than 225° F  Surface speeds exceeding 600 feet per minute (fpm).  2300 rpm for 1 inch diameter shaft  1150 rpm for 2 inch diameter shaft

57 Rotary Seals

58 Lip Seals Lip seals work well in high speed low pressure rotating shafts

59  Ball and roller bearing protection  As little as 0.002% water in lubrication oil can reduce ball bearing life by 50%  Solid particles cause rapid damage to the bearing races. Main Application of Lip Seals

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62 The purpose of the spring is to provide a uniform load on the lip The spring keeps the seal lip in contact with the shaft during higher speeds and also overcomes compression set and wear of the lip material.

63  There is a tendency for liquids to be pumped from the low angle side towards the high angle side. Underneath the flattened area a thin fluid film is formed. Its thickness must be between 1 and 3 µm to avoid leakage

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65 Primary function is retention Primary function is exclusion

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68  To minimize wear  The contact pressure should be as low as possible.  Shaft surface should be smooth to µm.  There must be enough fluid to form a hydrodynamic film  Fluid pressure must be low (0-3 psi ) Lip Seals

69 V-Seals

70 Speeds up to 5000 fps Pressures up to 150 psi Material: PTFE, graphite Flexi-Lip Rotary Seals

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76  Metallic seals go where polymers cannot  High temperatures (Above 400 to 1800 Degree F)  Cryogenic temperatures (below −238 °F)  High pressures (3000 psi to psi)  High speeds Metallic Seals

77 Metal Seals

78 C-Ring and Energized C-Ring

79 E-Ring and O-Ring

80 U-Ring and Metal Wire

81 Combustion Engine Piston Rings First compression ring (1) Second compression ring (2) Oil scraper ring (3)

82  Compression ring  Seals the gases in the cylinder  Gas pressure forces the ring against the cylinder wall  Wiper ring (secondary compression ring)  Seals the gases that escape the compression ring  Wipes excess oil from cylinder wall  Oil ring  Made of two thin rails with slots  Wipes excess oil from cylinder walls through port holes Piston Rings

83 Labyrinth Seals

84 Labyrinth Seal

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86  Mechanical Seals Rotating Elements

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